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Summary Full report
Marlbank-Cuilcagh Mountain Region; Western Marlbank
Rec. Number:1157File Number:  
ESCC:IC
Locality Type:Karst Status:
Grid Reference: H1034 Approximate
County: Fermanagh District:Fermanagh District Council
Period:Quaternary, Carboniferous
Stages:Asbian, Holocene, Visean
Lithostrat:Cloghan Hill Limestone Member, Dartry Limestone Formation, Glenade Sandstone Formation, Glencar Limestone Formation, Knockmore Limestone Member, Meenymore Formation
Site Description

TO BE ADDED
Highlights:
The western Marlbank area contains extensive well developed doline and limestone pavement fields, many of which are in a good state of preservation. Although explored cave is limited, considerable potential exists for major discoveries.
Introduction:
The Western Marlbank area covers the area between the presumed western edge of the Marble Arch System catchment and the border with the Republic of Ireland. There are a number of karst hydrological catchments within this area, of which two lie partially within Northern Ireland and partially within the Republic of Ireland.
Major speleological sites: Hammer Pot (H1015 3477), Hanging Rock Risings - East Rising (H1045 3663), West Rising & Pollnasalac (H1042 3663), Polltullyard (H0944 3241), Legacapple (H0965 3496).
Minor speleological sites: Revolution Pot (H1035 3524), Dave's Hole (H0954 3535), Tullynakeeragh Gravel Lake (H0976 3188), Killykeeghan Pots, Marlbank Rising, Gortaree Sink (H0836 3526).
Total surveyed cave: 750m+.
Area of exposed limestone pavement: 1,000,000m2.
Description:
I - Hydrology
A number of tracing experiments have been conducted in the Western Marlbank area and, at present, three karst hydrological units are presumed to exist. These are the Shannon Pot catchment to the south of the Cuilcagh Dyke and the Hanging Rock and Ture Rising catchments to the north of the Cuilcagh Dyke. The Hanging Rock rising catchment lies to the east of the area, and the Ture Rising catchment to the west of the area, north of the Cuilcagh Dyke. The boundary between the Hanging Rock and Ture Rising catchments is unknown and an element of mixing may be present. The bulk of the Shannon Pot and Ture Rising catchments lie in the Republic of Ireland, as do both the resurgences.
(i) Shannon Pot catchment in N. Ireland
A small stream rising on the Namurian shales to the west of Tiltinbane flows northeast from County Cavan into County Fermanagh. At H09413186 the stream splits, part of the water flowing back into County Cavan to sink at Pollahune and the remainder of the water sinking at Tullynakeeragh Gravel Lake, a sandstone walled doline/sinkhole. Both sinks have been traced to Shannon Pot, with the Gravel Lake water entering Shannon Cave via Mistake Passage (Gunn, 1985).
In addition, a small stream draining the Tullyard townland area sinks at Polltullyard. This stream has been traced to JCP passage in Shannon Cave, and subsequently to Shannon Pot.
(ii) Ture Rising catchment in N. Ireland
No sites in Northern Ireland have, as yet, been traced to Ture Rising although it is postulated that water sinking at Gortaree flows to this rising.
(iii) Hanging Rock
Gunn (op. cit.) has traced Legacapple to the Hanging Rock Risings. No other traces have been completed. Hanging Rock Risings consists of two resurgences, the East Rising and the West Rising. The West Rising frequently dries up.
II - Underground Karst
(i) Shannon Pot System Tullynakeeragh Gravel Lake: Gravel Lake is an ~10m diameter circular depression surrounded by 1m high Glenade Sandstone walls along its eastern margin. The floor of the depression is composed of flat clasts of fine siltstone and shale debris derived from the overlying clastic sequence. A small stream sinks at the eastern margin in normal conditions and in flood conditions the water backs up to form a small pond. Polltullyard: At Polltullyard a small stream sinks in a 6m deep doline with a 2m limestone scarp on the southeastern side. At the base of the scarp 20m of passage developed in the cherty facies of the Dartry Limestone can be followed to the top of a 30m shaft.
Polltullyard: entrance passage in cherty facies of the Dartry Limestone.

Polltullyard: caver descending 30m shaft.

Polltullyard: caver descending 30m shaft.
The shaft and the passages below are developed in the Knockmore Limestone Member. The cave contains many deposits of cobble and boulder sized sandstone clasts which appear to be related to large dolines on the surface. At the bottom of the shaft the stream sinking on the surface is met. Downstream the stream quickly disappears into pebbles and boulders. To the north a boulder slope descends for about 25m, bounded by a solid limestone wall on the north and on the south by massive gritstone boulders. This leads to a boulder filled chamber from where the stream disappears into a narrow rift. An abandoned passage runs parallel to the stream and after 30m encounters a choke of gritstone cobbles. Upstream an awkward 4m climb enters 200m of well developed phreatic/vadose canyon passage.
Polltullyard: the upstream canyon passage showing large scalloping.

Polltullyard: the upstream canyon passage showing large scalloping.

Polltullyard: the upstream canyon passage showing large scalloping.
There are a total of four inlets. Killykeeghan Pots: There are a large number of shakeholes and small sinks in the Killykeeghan Townland area which are believed to connect to the Shannon Cave System. (ii) Ture Rising System Gortaree Sink consists of ~60m of passage ending in a sump and is believed, although not proved, to drain to Ture Rising. (iii) Hanging Rock System The Hanging Rock System is believed to be an extensive, dominantly phreatic system, with sinks in the Western Marlbank area feeding the Hanging Rock Risings. Legacapple: A large stream (draining Legalough) sinks in a boulder collapse. Hammer Pot: Hammer Pot consists of a series of short tight vertical sections interspersed with small chambers. At the bottom of the pot is a sump which has been dived into an extensive series of muddy active phreatic passages with a large water flow through this part of the cave. Hanging Rock Risings: Hanging Rock Risings are located at the western end of Hanging Rock cliff. There are two risings, the East Rising and the West Rising. The West Rising frequently dries up. Pollnasalac is a short cave associated with the West Rising, consisting of 30m of dry passage ending in a sump which has been dived for 25m. Divers' reports suggest that this is normally a static sump. Revolution Pot: A 20m pot with 30m of passages ending in a dig with the sound of water. At the opposite end are small crawls and chambers and a high-level mud filled oxbow. III - Surface karst Surface karst features in the Western Marlbank are generally restricted to limestone pavements and dolines. One well developed dry valley, The Fosstra, is present, as are a large number of perched erratic boulders in the Killykeeghan area. Tullynakeeragh Gravel Lake is the only subadjacent karst doline in Northern Ireland. Karren Fields and Doline Fields: There are a number of extensive doline fields in the Western Marlbank area although a considerable area has been destroyed by land improvements. It is difficult, at present, to determine the exact extent of well preserved doline field and free karren in the western Marlbank area and an in depth survey of the area would be required to enable proposals for designation to be made. Areas known by the authors to be, at present, in a good state of preservation are contained within the Crossmurrin and Killykeeghan nature reserves and on Cullentragh Hill. Dry Valley: The Fosstra is a northeast oriented 5m wide shallow gorge and 30m wide dry valley, the valley lying to the northeast of the gorge. The dry valley is approximately 25m deep. There are two relict caves associated with the valley. Perched Erratics: A large number of sandstone boulders perched on limestone pedestals are present in Killykeeghan townland, especially the Tullyard area and also within the National Nature Reserve.
Importance:
The western Marlbank area contains numerous well developed and preserved doline fields and partially vegetated limestone pavements, of which the best developed are in the Crossmurrin- Killykeeghan and Gortaree-Cullentragh-Cloghan Hill areas. These doline fields and partially vegetated limestone pavements are the most concentrated in Northern Ireland. There is presumed to be an extensive cave system developed within the area, although only a small portion of this system has been explored.
Interpretation:
The western Marlbank contains a number of karst drainage systems which are, at present, not fully defined. Little cave passage has been discovered in this area and this may be due to a variety of factors. Glacial drift is more extensive in the Western Marlbank choking many of the sinks and dolines, streams tend to be smaller that those to the east and there is evidence from tracing experiments and cave diving exploration to suggest that much of the cave passage to the north of the Cuilcagh Dyke is phreatic in nature.
(i) Shannon Pot System
Polltullyard and the Killykeeghan pots have been proved to form part of the Shannon Cave System and are vadose stream sinks feeding water to this system. The presence of extensive deposits of sandstone cobbles and boulders within the cave, closely related to large dolines on the surface, indicates that there has been significant collapse or choking of shafts entering the cave associated with these dolines.
(ii) Hanging Rock System
Here, the system is thought to be largely phreatic in nature, this phreas being controlled by ponding of water, due to the southerly dip of the Dartry - Glencar Limestone contact and the presence of the Cuilcagh Dyke to the south. At Hanging Rock Risings, the West Rising and Pollnasalac are interpreted as flood overflows for the East Rising.
(iii) The Fosstra
The Fosstra is interpreted as a permafrost feature, formed during surface flow.
(iv) Perched erratics
These are glacially derived sandstone boulders which are perched on limestone pedestals, formed due to dissolution of the limestone surrounding the area of the boulder. The pedestal is formed as it is protected from dissolution by the boulder.
Conclusions:
CONCLUSION
The Western Marlbank area contains doline fields and partially vegetated limestone pavements which are some of the best developed and preserved in Northern Ireland. Extensive unexplored cave passage exists within the area.
Notes:

For site specific information see;
Key Site 367 - Hammer Pot Key Site 368 - Hanging Rock Risings-East Rising Key Site 369 - West Rising and Pollnasalac Key Site 370 - Polltullyard Key Site 371 - Legacapple Key Site 372 - Revolution Pot Key Site 373 - Dave's Hole Key Site 374 - Tullynakeeragh Gravel Lake Key Site 375 - Killykeeghan Pots Key Site 376 - Marlbank Rising Key Site 377 - Gortaree Sink.
For information and reference lists on the systems and features of other karst areas within the Marlbank-Cuilcagh Mountain Region see;
Key Site 1153 - East Cuilcagh Key Site 1154 - Tullyhona, Brookfield and Trien Key Site 1155 - Prod's Pot - Cascades Rising Area Key Site 1156 - Marble Arch Karst.
BIOLOGICAL INTEREST
No fauna has been previously recorded from this area and no collection was made in the course of the current programme.

Keywords
Minerals:Calcite
Rocks:Dolerite, Limestone, Sand, Sandstone, Shale
FossilGroups:No data
Fossil List:
Products:
Structures:bedding, dyke, fault, joints, rift
Relations:No Data
Geomorph:cave, clastic sediments, dendritic river cave, doline, drift, dry valley, karren, limestone pavement, sinkhole, speleothem
Paleoenv:
NonGeol: 
Measurements
Length:750 mWidth:No dataHeight:No data
Depth:No dataArea:1,000,000 m  
Access
Approach:Not entered
Restrictions:Not entered
Planning: 
Management:The Western Marlbank is predominantly upland rough pasture. Internal threats: At present, the only extensive cave known in the area is Polltullyard. This is popular with cavers as it is an excellent site for vertical caving practice. The cave, while generally medium energy, contains no speleothems and clastic sediments are largely composed of mobile boulder and cobble grade sandstone clasts. The other minor caves explored to date in the Western Marlbank receive few visits from cavers. External threats: External threats to the Western Marlbank karst are related to land improvement and pollution of the aquifer by agricultural effluents (fertilizers, silage and slurry). Potential problems may arise in the future from human waste effluent disposal. At present there is no evidence to suggest that these are responsible for any deterioration in the water quality. Considerable areas which included well developed doline fields and limestone pavement have been improved, involving infilling of dolines and covering or removal of the limestone pavement.
Development: 
Threats:Accidental damage by cavers; pollution by agricultural and human effluents; land improvement practices.
Uses
Uses:Upland rough pasture; caving.
Potential:Considerable potential exists for further discoveries in the Western Marlbank area. It is certain that any progress made in this area will involve surface excavations at promising potholes and sinks and/or diving.
Educ. Level:Not entered
References

Map(s):

The following areas have been marked on OSNI 1:10,000 sheets 243 and 228; / / WM 1. Tullynakeeragh Gravel Lake. / WM 2. Polltullyard, Tullyard Karren and the Killykeeghan Pots. / WM 3. Crossmurrin and Killykeeghan Doline - Karren Fields. / WM 4. Gortaree-Cullentragh-Cloghan Hill Karren Fields.

Map No:None entered
Rec Type ESCR report Recorder:  
Enterer: E M Porter
Updates: 28 APR 97 / 26 FEB 97
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